Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer sheets that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass typically refers to a transparent laminate comprising a poly(vinyl butyral) sheet disposed between two panes of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening.
Poly(vinyl butyral) is commonly produced through, for example, extrusion processes. Extrusion results in the formation of a continuous sheet of poly(vinyl butyral). Typically, this sheet is rolled for storage and shipping. The sheet can also be cut and stacked for storage and shipping.
Poly(vinyl butyral) sheet, whether in roll form or in stacked form, can tend to stick to itself or “block” at temperatures that can be encountered before and during the laminating process. This blocking is generally not desirable, and can lead to increased production costs.
Conventional attempts to enhance the blocking resistance of poly(vinyl butyral) sheets include mechanical roughing of the sheet surfaces (for example, embossing), applying a powder such as sodium bicarbonate to the sheet surfaces in contact with each other, and chemically treating the surfaces of the poly(vinyl butyral) sheeting, among others. Such surface treatments can, however, often create undesirable handling or adhesion properties, and are often difficult and/or expensive to implement.
In other conventional methods used to prevent blocking, poly(vinyl butyral) sheeting can be interleaved with another sheet material, such as polyethylene, or can be stored and transported under refrigeration, for example at temperatures from about 5° C. to about 15° C. For some compositions of poly(vinyl butyral) sheeting, however, such as poly(vinyl butyral) sheeting having relatively high plasticizer content, these anti-blocking techniques may not produce optimal results.
Another technique for preventing blocking entails incorporating anti-blocking materials directly into the poly(vinyl butyral). Incorporation of such materials into the poly(vinyl butyral), however, can adversely affect the optical properties of the resulting laminate or the adhesive properties of the finished poly(vinyl butyral).
Accordingly, further improved compositions and methods are needed to enhance the blocking resistance of polymer sheets, and specifically poly(vinyl butyral) sheets, without adversely affecting the optical clarity of the finished laminates of the glass or adhesion properties of the resulting poly(vinyl butyral) sheet to glass.